1. Field of Art
The present disclosure relates to communications systems, apparatus and methods therefore. In particular, but not exclusively, the present disclosure relates to private mobile radio (PMR) communications systems such as, without limitation, the Terrestrial Trunked Radio (TETRA) system and the P25 or APCO-25 Land Mobile Radio system.
2. Description of the Related Art
PMR communications systems, and TETRA in particular, are suitable for use by emergency services, government agencies, public safety networks and the military where security and reliability of communications is of paramount importance. PMR systems are also used in commercial enterprises, for example, in distributed or wide area locations such as large industrial sites, mine environments and the like.
A PMR system often comprises a single main site over which radio communications signals are transmitted from a Base Transceiver Station (BTS). Such a site may be termed a “cell” or “main site”. Mobile transceiver units, termed “Mobile Stations (MS)” in the TETRA standard lexicon, receive and transmit radio communications from and to the BTS when in the site/cell coverage area. In common with many radio communication systems, PMR radio systems such as TETRA can suffer from gaps in coverage due to the terrain, intervening structures such as buildings and within buildings or tunnels for example. To overcome the poor signal conditions repeater stations known as Trunked Mode Operation (TMO) repeaters are used to extend coverage into the affected area to fill gaps in the outdoor coverage or to extend coverage into buildings and tunnels.
However, good isolation between the receive and transmit antennas of the repeater station is necessary otherwise the repeater station signals may go into oscillation within the circuitry, caused by a signal being transmitted from the transmit antenna being received by the receive antenna and the repeater station repeating and transmitting that signal again and then received and repeated again and again until the repeater station fails.
Aspects and embodiments of the present configurations were devised with the foregoing in mind.